Process of concentrating dilute nitric acid.



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EIVIIL COLLET'I, CHRISTIANIA, NORWAY, ASSIGNOR TO NORSK-HYDBOELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NORWAY.'

- PROCESS OF CONCENTRATING DILUTE NITRIC ACID.

N 0 Drawing. Original application enable others skilled in the art to which it appertains to make and use the same.

This invention relates to the concentration of acids by boiling an acid in distillation vessels and introducing acid vapors containing moisture into a drying tower chargedwith a drying agent, such as concentratedsulfuric acid, which absorbs the moisture 'or water vapor and permits the concentrated-acid. vapor to escape therefrom,

and is a division of my application for pat ent, Serial No. 7 57,252, filed March 27th,

. By operating in the manner above, described it has been found that it is difiicult to regulate the temperature so that the desired concentration is obtained. The temperature is liableto rise too high, and thus allow water vapor, which should otherwise be absorbed, to escape with the acid vapors and give a too low concentration, with the accompanying loss of energy, and increased costs for further concentration.

I have found that I can reliably control the temperature in the drying tower in a very simple manner. The drying medium, sulfuric acid, for instance is usually supplied at the top of the tower in a heated condition. I then introduce a cooling medium into the tower at a lower point, which may be cold sulfuric acid, cold nitric acid, or a cold mixture of the two acids. The acid vapors to be concentrated or dried are introduced at the bottom of the drying tower. At the point or zone of the appa ratus where it has been found by experience that the highest temperature prevails, or at a point below'the top of the tower which by Specification of Letters Patent.

Patented Get. 26, m5.

filed March 27, 1913, Serial No. "757,252. Divided and this application filed June 15, 1915.

Serial No. 34,308.

amount and temperature of the cooling agent introduced at this point the temperaf ture in the drying apparatus can easily be maintained within the limits desired. When cold sulfuric acid is introduced at the zone of maximum temperature it absorbs heat and at the same time assists in the concentration or drying. \Vhen introducing cold nitric acid alone, this acid must have a rather high concentration for inst; about 60 per cent. in order that its content of Water shall not by contact with the drying agent (sulfuric acid) evolve injurious heat and thus counteract the cooling action to be attained.- This concentrated nitric acid when cold, acts as a cooling agent by absorbing heat from the hot zone, and also causes an absorption of heat by vaporization, the acid vapor mixing with and escaping with nitric acid vapors that are being concentrated. When a cold mixture of sulfuric and nitric acids is used, the combined actions of the two acids are exerted on the vapors to be dried.

Claims:

1. In the process of concentrating nitric acid vapors by absorbing moisture there from -in an apparatus employing sulfuric acid as a drying agent, the improvement which comprises introducing concentrated nitric acid into said apparatus between the point where the vapors enter the latter and the point where the vapors escape.

2. In the process of concentrating nitric acid vapors by absorbing moisture therefrom in an apparatus employing sulfuric acid as a drying agent, the improvement which comprises introducing cold concentrated nitric acid into said apparatus between the point where the vapors enter the latter and the point where the vapors escape.

3. In the process of concentrating acid vapors by absorbing moisture therefrom in an apparatus employing a suitable drying agent, the improvement which comprises introducing, at a point below the top of the tower, into the current of the acid vapors to be dried, a vaporizable liquid that does not affect the concentration of the acid vapors.

4. In the process of concentrating acid vapors by absorbing moisture therefrom in as my invention, 1 have signed my name in an apparatus employing 1a sfilitable drying 131 Hence 01' two subscribing witness.

a 'eiit the improvement W iic com prises inv w r r ti oduizing, at the zone of maximum tempem- EMIL COLLE l tux-e a vaporizable liquid that does not affect Witnesses:

the concentration of the mid vapors. lil. E. GUTTODRUSER,

In testimony that I claim the foregoing C. F HANSEN. 

